In the field of the vehicle control technology, there is often used a by-wire system. The by-wire system electrically controls an actuator, which changes an operational state of a vehicle, through a by-wire control circuit in response to a command of a driver (user) of the vehicle. For example, a shift-by-wire system, which shifts a shift range of an automatic transmission of the vehicle in response to a command of the driver of the vehicle, is known. In the shift-by-wire system, the shift range is shifted by, for example, rotating an electric actuator to drive a range shift mechanism of the automatic transmission. The range shift mechanism includes a detent plate, a manual valve and a detent spring. The detent plate is rotated by an actuator. The manual valve is operable synchronously with the detent plate. The manual valve sets a shift range of the automatic transmission to a corresponding range, which corresponds to the rotational position of the detent plate. The detent spring includes a limiting portion, which is adapted to be fitted into a corresponding one of recesses formed in the detent plate to limit the rotation of the detent plate and thereby to fix the shift range of the automatic transmission to the corresponding predetermined range. The actuator includes an electric motor unit and a speed reducing unit. The motor unit is rotatable at a high speed. The speed reducing unit reduces the rotational speed of the motor unit and outputs the rotation of the reduced rotational speed. In a case where a brushless motor, such as a switched reluctance (SR) motor, is used in the motor unit, an incremental encoder (also referred to as an increment type encoder) is typically provided in the actuator. The incremental encoder outputs a pulse signal, which corresponds to an amount of change in the rotational angle of the electric motor unit. A rotational state of the motor unit is sensed based on the pulse signal outputted from the encoder, and the sensed state of the motor unit is used in a feedback control operation of the motor unit. In this way, the rotation of the motor unit can be appropriately controlled.
JP2009-162309A discloses a shift-by-wire system, which includes an output angle sensing means that senses a rotational angle of an output shaft of an actuator. An actual range of an automatic transmission is determined based on a signal outputted from the output angle sensing means, which indicates the rotational angle of the output shaft of the actuator. In this shift-by-wire system, a range determination extent in the middle of rotating the motor unit, i.e., in the middle of shifting the shift range of the automatic transmission is set to be larger than a range determination extent in a stop state of the motor unit. However, in the shift-by-wire system of JP2009-162309A, the actual range is determined even during the period of rotating the motor unit. Therefore, an erroneous determination of the actual range may possibly occur due to sensing variations.